Water developers in California and other coastal communities throughout the world are increasingly considering seawater desalination as a potential source of water for municipal and industrial supply. Limited ground water supplies in the coastal areas, poor inland ground water quality, and decreasing reliability of imported water have made seawater desalination a viable consideration. Seawater desalination has been made even more viable through more cost-effective and efficient subsurface intake systems and water treatment technologies.
Slant well drilling is included in the practice of drilling non-vertical wells. Non-vertical wells are typically used in the petroleum industry and are also known as horizontally directionally drilled wells (HDD wells). Slant wells are also used in other applications, such as drilling beneath roadways or rivers in order to provide conduits for facilities. Slant well desalination subsurface intake systems present significant advantages over traditional open water desalination plant intakes. These advantages include avoidance of entrainment and impingement impacts to marine life, reduction or elimination of costly reverse osmosis pretreatment, and reduction or elimination of permanent visual impacts. Slant well systems are buried systems (i.e. there are little or no visual impacts on the surface), as the wells and connecting pipelines are typically completed below the land surface.
In the past, slant well technology has not been successfully applied to subsea construction of desalination feedwater supplies, as the well screen slots have become clogged during pumping. Once the well screen slot openings are clogged, it becomes difficult or impossible to continue to pump water. Accordingly, there is a need for a reliable slant well system that is able to supply water from near-shore or subsea aquifers to a desalination plant without becoming clogged with fine-grained materials (e.g., fine sands and silts) over time. There is also a need for a method of constructing such a system—especially at low angles below horizontal in order to minimize impacts to inland fresh water sources. The present invention satisfies these needs and provides further related advantages, especially with regard to regulation of feedwater salinity.